Render yellow colored object as blue (design oriented question)
When using colored light, you have to remember that it affects the color of objects.  If you use a blue light in real life, most colors will not appear correctly.  If you look at the color chart on this page:

http://www.d.umn.edu/~mharvey/handbook5607.html

...you can see that under blue light, red, green, and yellow pigments will appear black.  Orange pigment appears dark brown.  Others just appear blue or darker blue.  It's just the science of light.

Here's a scene in Blender with pure white light:


The same scene with blue light:


and green:


and red:


If you must use a blue light, I'd make your dunes white or a shade of gray instead of yellowish-orange.

However, most scenes aren't lit with a single light source.  What you could do is add a touch of "moonlight" by adding a second light.  Here I made the blue light a "hemi" light, and then added a "sun" light that is light gray:



It's still blue and dark, but you can see the different colors again.